Our central hypothesis is that host HLA Class I molecules regulate the phenotype and function of NK subsets and the repertoire of NK receptors. We propose to test the following hypotheses: (1) host HLA class I phenotype influences the repertoire of NK subsets, (2) host HLA class I phenotype affects NK receptor cell surface density and (3) NK cell repertoire in primary cells differs from NK clones. These hypotheses will be tested by three innovative methods: (a) four-color FACS for complex receptor expression on NK cells, (2) single cell RT-PCR to determine the repertoire of NK receptors in individual NK cells and (3) the surface expression of NK receptors on NK subsets by a quantitative FACS assay. Finally we will compare the NK repertoire of primary peripheral blood cells with that of NK clones generated from cells of donors who are homozygous or heterozygous for HLA-B or C/MICA specificities. We will also test NK clones for cytotoxic activity against a panel of self HLA class I-transfected target cells to determine whether there is an association between NK receptor phenotype and NK function. The data of the proposed studies should provide conclusive evidence for the HLA-dependent changes in the sizes of specific NK cell subsets, the repertoire of specific NK receptors and NK clone function. Understanding the genetic factors that influence the development of NK subsets and the receptors that define their repertoire will be important in the assignment of risks for rejection or for graft-versus-host reaction following bone marrow transplantation or NK-mediated killing of virus-infected cells.